#define _CRT_SECURE_NO_WARNINGS 1

# include<iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int ret = n % 2 ? n : -1;
    cout << ret;
    return 0;
}
# include<iostream>
using namespace std;

int main()
{
    int a, b, n;
    cin >> a >> b >> n;
    int flg = n - a - b;
    if (flg >= 0 && flg % 2 == 0)
    {
        cout << "YES";
    }
    else
    {
        cout << "NO";
    }
    return 0;
}
# include<iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    string ret = n > 50 && n % 2 == 0 ? "yes" : "no";
    cout << ret;
    return 0;
}

# include<iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    if ((n % 4 == 0 && n % 100 != 0) || (n % 400 == 0))
    {
        cout << "yes";
    }
    else
    {
        cout << "no";
    }
    return 0;
}

# include<iostream>
using namespace std;

int main()
{
    int pos = 0, neg = 0, tmp = 0;
    for (int i = 0; i < 10; ++i)
    {
        cin >> tmp;
        if (tmp > 0)
        {
            ++pos;
        }
        else if (tmp < 0)
        {
            ++neg;
        }
    }
    printf("positive:%d\nnegative:%d", pos, neg);
    return 0;
}

# include<iostream>
using namespace std;

int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    if ((a + b + c) * 1.0 / 3 >= 60)
    {
        cout << "NO";
    }
    else
    {
        cout << "YES";
    }
    return 0;
}

# include<iostream>
using namespace std;

int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    printf("The maximum number is : %d\n", max(a, max(b, c)));
    printf("The minimum number is : %d", min(a, min(b, c)));
    return 0;
}

